16 healthy volunteers of both sexes, age 18 to 45 years, will be enrolled. The mean dose necessary to suppress the Dobutamine induced heart rate increase of at least 30 bpm above baseline rate (maximum heart rate app. 110 bpm) by at least 20 bpm will be calculated for AOP200704 and Esmolol and the dose/efficacy relation of both agents to each other will be calculated for the steady state condition. For both drugs the time to reach a decrease of 10 bpm, 20 bpm and the maximum effect will be calculated. In addition the mean time to increase in 10 and 20 bpm and the time to reach maximum heart rate (increase of 30 bpm above baseline or more) after termination of infusion will also be assessed for both drugs. Blood pressure values will be compared for all above mentioned time points where heart rate is assessed for pharmacodynamics.The study will consist of a screening, cross-over 1, cross-over 2 and end-of-study visit.